1. Field of the Invention
The present invention relates to a multiple-effect absorption refrigeration system. More particularly, the present invention relates to a single loop, triple-effect absorption refrigeration system.
2. Description of the Related Art
Absorption refrigeration systems are generally used to cool commercial buildings. For example, a single-effect absorption system typically comprises an evaporator, an absorber, and a generator and condenser pair. In this system, a refrigerant fluid in the evaporator absorbs heat from the air in the commercial building or enclosure being cooled, upon flashing to vapor. The refrigerant vapor flows to an absorber, where it mixes with a strong refrigerant-absorption solution (higher ratio of absorption fluid to refrigerant), forming a weak refrigerant-absorption solution (lower ratio of absorption fluid to refrigerant). The weak refrigerant-absorption solution is then pumped to a generator, where the solution is heated by an outside source referred to as primary heat. Typical sources of primary heat include a fuel burner, low-pressure steam, or hot water. This heating boils off some of the refrigerant, separating the solution into a refrigerant vapor and a strong refrigerant-absorption solution. The refrigerant vapor is then condensed to refrigerant fluid in the condenser and routed back to the evaporator. The strong refrigerant-absorption solution returns to the absorber. Single-effect absorption refrigeration systems such as that described above are extremely inefficient, having a thermal Coefficient of Performance (COP) of approximately 0.7.
A more modern approach uses a double-effect absorption refrigeration system. In this latter system, the single generator and condenser pair is replaced by two generator and condenser pairs (i.e., a high temperature generator and condenser pair, and a low temperature generator and condenser pair). A weak refrigerant-absorption solution is pumped to both generators. Primary heat is supplied to the high temperature generator to boil off some refrigerant vapor from its refrigerant-absorption solution. This refrigerant vapor is condensed in the high temperature condenser. The heat of condensation from the high temperature condenser is used to heat the refrigerant-absorption solution in the low temperature generator, in order to boil off some refrigerant vapor from its refrigerant-absorption solution. This refrigerant vapor is condensed in the low temperature condenser. In this manner, the primary heat input to the system is utilized twice to generate refrigerant vapor. As a result, the double-effect absorption refrigeration system is much more efficient than its single-effect counterpart, having a thermal COP of approximately 1.2.
In recent years, experiments have been conducted with triple-effect absorption refrigeration systems, utilizing three generator and condenser pairs (i.e., a high temperature generator and condenser pair, an intermediate temperature generator and condenser pair, and a low temperature generator and condenser pair). Various triple-effect absorption refrigeration systems will be described below.
In one such triple-effect absorption refrigeration system, a single absorber provides a weak refrigerant-absorption solution to three generators connected in series. The generators include high, intermediate, and low temperature generators. Because of their series connection, the refrigerant-absorption solution flowpath direction is from the absorber to the high temperature generator, then to the intermediate temperature generator, and then to the low temperature generator. In each generator, refrigerant vapor boils off to its paired condenser: high temperature condenser, intermediate temperature condenser, or low temperature condenser, respectively. In order to further improve thermal performance, the high temperature condenser is coupled with the intermediate temperature generator, and the intermediate temperature condenser is coupled with the low temperature generator. This coupling is known as double-condenser coupling (DCC). Hence, this system is referred to as a triple-effect absorption refrigeration system with DCC. Multiple heat exchangers transferring heat from the strong refrigerant-absorption solution returning to the absorber, to the weak refrigerant-absorption solution flowing to the generators, can also be provided in the series flowpath. The thermal COP for such a system is approximately 1.60 to 1.65.
In a similar triple-effect absorption refrigeration system with DCC, a single absorber provides a weak refrigerant-absorption solution to three generators connected in inverse series. Once again, the generators include high, intermediate, and low temperature generators. Because of their inverse series connection, the refrigerant-absorption solution flowpath direction is from the absorber to the low temperature generator, then to the intermediate temperature generator, and then to the high temperature generator. Multiple heat exchangers transferring heat from the strong refrigerant-absorption solution returning to the absorber, to the weak refrigerant-absorption solution flowing to the generators, can be provided in the inverse series flowpath. The thermal COP for such a system is approximately 1.68 to 1.72.
In another similar triple-effect absorption refrigeration system with DCC, a single absorber provides a weak refrigerant-absorption solution to three generators connected in parallel. Once again, the generators include high, intermediate, and low temperature generators. Because of their parallel connection, the refrigerant-absorption solution flowpath direction is from the absorber simultaneously to the high, intermediate, and low temperature generators. Multiple heat exchangers transferring heat from the strong refrigerant-absorption solution returning to the absorber, to the weak refrigerant-absorption solution flowing to the generators, can be provided in the parallel flowpath. The thermal COP for such a system is approximately 1.70 to 1.74.
In yet another similar triple-effect absorption refrigeration system with DCC, a single absorber provides a weak refrigerant-absorption solution to three generators connected in inverse parallel-series. Once again, the generators include high, intermediate, and low temperature generators. Because of their inverse parallel-series connection, the refrigerant-absorption solution flowpath direction is from the absorber simultaneously to the low and intermediate temperature generators, then from the intermediate temperature generator to the high temperature generator. Multiple heat exchangers transferring heat from the strong refrigerant-absorption solution returning to the absorber, to the weak refrigerant-absorption solution flowing to the generators, can be provided in the inverse parallel-series flowpath. The thermal COP for such a system is approximately 1.72 to 1.78.
Another related triple-effect absorption refrigeration system with DCC includes two evaporator and absorber pairs. Mixed refrigerant-absorption solution is simultaneously pumped from the first absorber to the low temperature generator and from the second absorber to the intermediate and high temperature generators. Various other configurations have been proposed using multiple evaporator and/or absorber configurations.
In each of these triple-effect absorption refrigeration systems, the high temperature condenser yields a high temperature condensate stream that is much hotter than ambient temperature. This condensate has been typically cooled down and then throttled to evaporation temperature.